The pace of the song is slow, with a reasonably complex guitar accompaniment in the key of D. In the latest version, there are 6 two-line verses broken into two sections by a 6-line bridge in the middle, which I then return to at the end of the song to bring it to a conclusion. I use the term ‘bridge’ rather loosely here, since I don‘t think that this song conforms to the formal definition of the term (as presented in Wikipedia, for example).
The first verse describes the classic English post box:
Post boxes....In the bridge section, I look back almost nostalgically to the time of dip pens and ink wells. I went to school in the days where each class had an Ink Monitor (a boy who was designated to walk around the schoolroom with a huge bottle or jar of ink, filling each individual well that was sunken into each pupil‘s desk. And, of course, there would be the blotting paper, too. I also think about the gradual demise of lickable glue on stamps and envelope flaps: all part of the letter-writing experience of yesteryear.
In England they are mainly red;
And dated by their royal crest.